ABSTRACT The primary role of the Mouse Genetics Core is to facilitate the use of mouse molecular genetics at MSK for in vivo studies of gene functions germane to cancer. Relevant fields in which MSK investigators develop and apply mouse models include: cell growth and behavior, stem cell biology, embryonic development, immunobiology, genome integrity, cancer biology, and experimental therapeutics. The MGC consists of 2 sections: the Transgenic/Embryology Group (TgG) and the Molecular Biology/Tissue Culture Group (MBTCG). Major services offered by the TgG include the production of genetically engineered mice (GEM) by pronuclear injection of DNA or CRISPR/Cas9 and by blastocyst injection of ES cells; cryopreservation and the long-term storage of GEM lines; strain rederivation or recovery through IVF and/or embryo transfer; performance of special embryological and animal surgical procedures; and the provision of GEM lines such as CRE and FLPe expressing strains. The specialized molecular biology services provided by the MBTCG include transgene DNA purification and genotyping of founder mice; the design and production of CRISPR/Cas9 reagents for mouse genome editing; and the identification and verification of alleles carried by gene edited mice. Services offered by the MBTCG also include performing all aspects of gene targeting in mouse ES cells and establishing ES cells from GEM lines. An integral role of the MGC is to provide consultation and training in the design and production of mouse models, ES cell culture, and mouse husbandry and genetics. Rapid advances in genome editing and sequencing technologies, in combination with the steady increase in translational research at MSK, have resulted in a significant upsurge in demand for MGC services. In addition, the Core continues to pursue and implement new technical developments that will expedite gene editing in mice; ongoing efforts include the use of commercially available synthetic gRNA components and the application of electroporation to deliver CRIPSR/Cas9 into mouse zygotes. Integrating such advancements into the Core?s services will undoubtedly increase the productivity and reduce staff time/effort to create GEM models for MSK investigators.